perf: Fix AUX buffer refcounting

Its currently possible to drop the last refcount to the aux buffer
from NMI context, which results in the expected fireworks.

The refcounting needs a bigger overhaul, but to cure the immediate
problem, delay the freeing by using an irq_work.

Reviewed-and-tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150618103249.GK19282@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e965cfae420725645349c4facd145828e4e59d13..d3dae3419b99566c127f1682b29f39bb184bbdb1 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4358,14 +4358,6 @@ static void ring_buffer_wakeup(struct perf_event *event)
        rcu_read_unlock();
 }
 
-static void rb_free_rcu(struct rcu_head *rcu_head)
-{
-       struct ring_buffer *rb;
-
-       rb = container_of(rcu_head, struct ring_buffer, rcu_head);
-       rb_free(rb);
-}
-
 struct ring_buffer *ring_buffer_get(struct perf_event *event)
 {
        struct ring_buffer *rb;

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 2deb24c7a40dd979313eb1fcff58044d2d948888..2bbad9c1274c3199338e653bbb5c8bd640815fa7 100644 (file)
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -11,6 +11,7 @@
 struct ring_buffer {
        atomic_t                        refcount;
        struct rcu_head                 rcu_head;
+       struct irq_work                 irq_work;
 #ifdef CONFIG_PERF_USE_VMALLOC
        struct work_struct              work;
        int                             page_order;     /* allocation order  */
@@ -55,6 +56,15 @@ struct ring_buffer {
 };
 
 extern void rb_free(struct ring_buffer *rb);
+
+static inline void rb_free_rcu(struct rcu_head *rcu_head)
+{
+       struct ring_buffer *rb;
+
+       rb = container_of(rcu_head, struct ring_buffer, rcu_head);
+       rb_free(rb);
+}
+
 extern struct ring_buffer *
 rb_alloc(int nr_pages, long watermark, int cpu, int flags);
 extern void perf_event_wakeup(struct perf_event *event);

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 96472824a752f76fe651ec1bfb7ab7a52411a12c..b2be01b1aa9dcb7a70792fa381c264b229a106d0 100644 (file)
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -221,6 +221,8 @@ void perf_output_end(struct perf_output_handle *handle)
        rcu_read_unlock();
 }
 
+static void rb_irq_work(struct irq_work *work);
+
 static void
 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
 {
@@ -241,6 +243,16 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
 
        INIT_LIST_HEAD(&rb->event_list);
        spin_lock_init(&rb->event_lock);
+       init_irq_work(&rb->irq_work, rb_irq_work);
+}
+
+static void ring_buffer_put_async(struct ring_buffer *rb)
+{
+       if (!atomic_dec_and_test(&rb->refcount))
+               return;
+
+       rb->rcu_head.next = (void *)rb;
+       irq_work_queue(&rb->irq_work);
 }
 
 /*
@@ -319,7 +331,7 @@ err_put:
        rb_free_aux(rb);
 
 err:
-       ring_buffer_put(rb);
+       ring_buffer_put_async(rb);
        handle->event = NULL;
 
        return NULL;
@@ -370,7 +382,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
 
        local_set(&rb->aux_nest, 0);
        rb_free_aux(rb);
-       ring_buffer_put(rb);
+       ring_buffer_put_async(rb);
 }
 
 /*
@@ -557,7 +569,18 @@ static void __rb_free_aux(struct ring_buffer *rb)
 void rb_free_aux(struct ring_buffer *rb)
 {
        if (atomic_dec_and_test(&rb->aux_refcount))
+               irq_work_queue(&rb->irq_work);
+}
+
+static void rb_irq_work(struct irq_work *work)
+{
+       struct ring_buffer *rb = container_of(work, struct ring_buffer, irq_work);
+
+       if (!atomic_read(&rb->aux_refcount))
                __rb_free_aux(rb);
+
+       if (rb->rcu_head.next == (void *)rb)
+               call_rcu(&rb->rcu_head, rb_free_rcu);
 }
 
 #ifndef CONFIG_PERF_USE_VMALLOC